This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Hypothesis 1: TNS reduces depressive symptoms in people with mild to moderate major depressive disorder. Specific Aim 1: Compare depression scale scores before and after 8 weeks of TNS. Hypothesis 2: TNS is well-tolerated and safe. Specific Aim 2a: Assess blood pressure and EKG before and during TNS. Specific Aim 2b: Monitor for adverse events during TNS. Hypothesis 3: TNS causes blood flow changes in the the bilateral thalamus, cerebellum, limbic system, hypothalamus and medulla. Specific Aim 3: In three subjects, compare H215O PET blood flow measurements before and after TNS.